The tumor suppressor p53 is recognized as an important regulator of apoptosis in acute and chronic neurological insults and neurodegenerative disorders. However, the downstream molecular consequences of p53 activation in neurons still remain obscure. Our proteomic analyses have demonstrated that DNA damage-induced neuronal apoptosis involves a p53-dependent increase in the expression of proteins that comprise histone deacetylase (HDAC) complexes. This data suggests that p53 might promote neuronal dysfunction/cell death by activating histone deacetylase activity. Our preliminary studies indeed demonstrate that histone deacetylase inhibitors protect against p53-mediated cell death. In contrast HDAC activity is generally elevated in cancer cells, and HDAC inhibition actually induces p53-dependent cell death. In the present application, based on this novel finding of the neuron-specific mode of HDAC inhibitor actions, we propose to test the hypothesis that p53-mediated cell death signaling in neurons is dependent on histone deacetylase activity by examining how HDAC inhibitors block neuronal cell death. We will specifically: 1) Determine if HDAC inhibitors selectively protect neurons from p53-mediated cell death, 2) Determine if HDAC inhibitors directly block p53 activation and/or transcriptional activity required for p53-dependent cell death in neurons; and 3) Determine if HDAC inhibitors prevent p53- dependent changes in mitochondrial integrity. The aims of this proposal will help us to better understand the molecular sites and mechanism of HDAC inhibitor action, which will enhance the utility of these inhibitors as therapeutic agents for neurological diseases and injury. PUBLIC HEALTH RELEVANCE: Histone deacetylase inhibitors protect neurons from dying in several mouse models of human neurodegenerative disease. However, the mechanism by which histone deacetylase inhibitors prevent cell death is not understood. A better understanding of how these compounds work and the types of diseases or injuries that they protect against would enhance their range of action and their effectiveness. We propose to determine how histone deacetylase inhibitors block neuronal cell death which could lead to the development of new therapeutic agents for treating neurological diseases and nervous system injury.